Led by Professor Antonio Politano from the University of L’Aquila, Italy the team together with beamline scientists from URANOS beamline has identified and characterized a new chiral material, CdAs2, which exhibits a rare Kramers-Weyl fermion. Chirality, which refers to the asymmetry in the spatial arrangement of molecules, plays a crucial role in a wide range of scientific fields, including biochemistry and materials science. Chiral crystals exhibit well-defined handedness due to the breaking of inversion, mirror, or any other roto-inversion symmetries.

CdAs2, a crystal composed of cadmium and arsenic, is a promising quantum material with potential applications in electronics, spintronics, and quantum computing. The researchers used a technique called angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic structure of CdAs2 and found that it exhibits a Kramers-Weyl fermion behavior, which is extremely rare in chiral materials. Fermions are subatomic particles that obey the Pauli exclusion principle, which states that no two identical fermions can occupy the same quantum state simultaneously. Kramers-Weyl fermions, named after physicists Hendrik Kramers and Hermann Weyl, are a type of exotic fermion that have recently been predicted to exist in certain topological materials. The Kramers-Weyl fermion is a type of particle that has both spin and momentum, and its behavior is protected by time-reversal symmetry. This property makes it a potential building block for novel quantum devices, as it can be used to carry information in a topologically protected manner.
The discovery of Kramers-Weyl fermions at CdAs2 is a significant breakthrough in the field of quantum physics. Not only does it provide further evidence of the existence of exotic fermions in topological materials, but it also opens up new avenues for research into the properties of these materials and their potential applications in future technologies.

Figure 1. Crystal structure and electronic band structure of bulk CdAs2. (a) Optimized primitive (left) and conventional (right) unit cells of CdAs2. (b) First Brillouin zone of the primitive cell. (c) Calculated electronic band structure without SOC effects. (d) Calculated electronic band structure including SOC effects. The Fermi level is set to zero and marked by a horizontal red dashed line. Cd and As atoms are represented by yellow and purple balls, respectively. The Kramers–Weyl nodes (d) are marked by yellow circles.

Written by: Antonio Politano, Natalia Olszowska

The publication can be found here:

F. Mazzola et al., Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers–Weyl Fermions, J Phys Chem Lett 14, 3120 (2023). doi: 10.1021/acs.jpclett.3c00005